Evaluate lisdexamfetamine dimesylate (LDX) augmentation of antidepressant monotherapy for executive dysfunction in partially or fully remitted major depressive disorder (MDD). This randomized, placebo-controlled study (NCT00985725) enrolled 143 adults (18-55 years) with mild MDD (Montgomery-Åsberg Depression Rating Scale (MADRS) score ≤ 18) and executive dysfunction (Behavior Rating Inventory of Executive Function-Adult Version (BRIEF-A) Self-Report Global Executive Composite (GEC) T score ≥ 60) on stable antidepressant monotherapy for ≥ 8 weeks. After 2 weeks of screening, participants were randomized to 9 weeks of double-blind LDX (20-70 mg/day) or placebo augmentation, followed by 2 weeks of single-blind placebo. The primary end point was change from baseline to week 9/end of study (EOS) in BRIEF-A Self-Report GEC T score; secondary assessments included the BRIEF-A Informant Report, MADRS, and treatment-emergent adverse events (TEAEs). Of 143 randomized participants, 119 completed double-blind treatment (placebo, n=59; LDX, n=60). Mean ± standard deviation (SD) BRIEF-A GEC T scores decreased from baseline (placebo, 74.2 ± 8.88; LDX, 76.8 ± 9.66) to week 9/EOS (placebo, 61.4 ± 14.61; LDX, 55.2 ± 16.15); the LS mean (95% CI) treatment difference significantly favored LDX (-8.0 (-12.7, -3.3); P=0.0009). The LS mean (95% CI) treatment difference for MADRS total score also significantly favored LDX (-1.9 (-3.7, 0.0); P=0.0465). TEAE rates were 73.6% with placebo and 78.9% with LDX; serious TEAE rates were 4.2 and 2.8%. In this trial, LDX augmentation significantly improved executive dysfunction and depressive symptoms in participants with mild MDD. The safety profile of LDX was consistent with prior studies in adults with attention-deficit/hyperactivity disorder.